Transformer apparatus



.March 2, 1943. Q E BOUCHER TRANSFORMER APPARATUS 4 Sheets-Sheet 1 Filed April 1o, 1940 f l LQ.

JAMin/raf? '/ZarZas' j? ,30mn B u W March 2, 1943. c. P. BOUCHER 2,312,857

TRANSFORMER APPARATUS Filed April 1o, 1940 4 sheets-sheet 2 March 2, 1943. P BQUQHER 312,867

TRANSFORMER APPARATUS Filed April l0, lQLlO -4 Sheecs-Shee'l; 3

g3 95 Ik," la@ MalCh 2, 1943- C. P. BOUCHER 2,312,867

TRANSFORMER APPARATUS Filed April 10, 1940 4 Sheets-Sheet 4 CizrZew Pcker w MW Patented Mar. 2, 1943 TRANSFORMEB APPARATUS Charles Philippe Boucher, Paterson, N. J., assignor to Boucher Inventions, Ltd., Washington, D. C., a corporation of Delaware Application April 10, 1940, Serial No. 328,970

3 Claims.

My invention relates to electrical transformer apparatus, and more particularly to electrical transformer apparatus for supplying two or more negative loads, as, for example, in the operation of a luminescent tube system.

One of the objects of my invention is to provide simple, practical and thoroughly reliable transformer apparatus for supplying a plurality of separate negative loads and for ensuring automatically that substantially no voltage difference exists between the secondary circuits throughout the entire cycle of operation, and also that the currents in the various circuits are substantially the same.

Another object is to provide compact, inexpensive and highly efficient transformer apparatus for supplying a plurality of negative loads and for energizing in a dependable manner the remainder of said loads after one or more of them has struck.

Another object of my invention is to provide a transformer system in which negative loads of either equal or unequal resistances may be operated from the same transformer.

A further object of my invention is the provision of a transformer apparatus of the character described which lends itself to rapid, eillcient and economical production employing a minimum of different parts and requiring a minimum of skill in construction, installation and repair.

Another object is the provision of transformer apparatus of the character indicated which is peculiarly adapted to withstand the varying conditions encountered in actual use, including short-circuiting and grounding, of the whole or parts of the apparatus, without damage to the apparatus and the consequent necessity for shutdown and replacement or repairs.

Another object is the provision of high Voltage transformer apparatus of the character indicated which supplies a plurality of separate loads in such a Way as to require a minimum amount of insulation.

Other objects will be obvious in part and in part pointed out hereinafter.

The invention accordingly consists in the combination of elements, features of construction, and arrangement of parts, and in the several operational steps, and in the relation of each of the same to one or more of the others, all as described herein, the scope of the application of which is indicated in the appended claims.

In the accompanying drawings:

Figure 1 is a schematic plan view and Figure 2 is a corresponding front elevation view of a transformer and tube assembly embodying my invention in which shunts for the four secondary coils mounted on H-shaped members are located on the external portion of the main core.

' Figure 3 is a diagrammatic representation of a transformer likewise embodying my invention but having the secondary coil shunts located internally of the main core.

Figure 4 represents a transformer similar to that shown in Figure 3 but having the secondary coils mounted on the main core bars instead of on the H-shaped members.

Figure 5 is a diagrammatic representation of a transformer according to my invention having internal shunts formed by integral parts of the central core bar.

Figures 6 and '7 represent transformers similar to that of Figure 5 but designed for mounting two instead of four secondary coils on the core. Like reference lcharacters denote like parts throughout the several views of the drawings.

As conducive to a clearer understanding of certain features of my invention, it may be noted at this point that in the operation of a luminescent sign or display employing one or more luminescent gas filled tubes of desired size and configuration, high potential electrical energy is required. Ordinarily the desired high potential electrical energy is supplied by alternatingcurrent transformer apparatus connected to a standard single phase sixty cycle source at either one hundred and ten volts or two hundred and twenty volts. In order to supply the highest possible potential across the terminals of a tube without exceeding the maximum potential to ground permitted by the Fire Underwriters, it has been the practice to energize each tube from two coils having their one ends'grounded placing the coils in series and their other ends connected to the tube. By this arrangement, each coil section may have induced in it a potential of about seven thousand ve hundred Volts to ground, which is approximately the maximum value permitted by the Underwriters, and yet the voltage across the tube terminals Will be about fifteen thousand volts.

In the operation of a single sign or luminous display, it is frequently necessary to use a plurality of luminescent tubes. In order that the energizing potential may not reach values in excess of those specified by the Underwriters, and since luminescent tubes have negative load characteristics and vary among themselves as to striking and operating potentials, each tube must have its own separate secondary winding. To

COTS.

result in an exceedingly high cost of equipment. Furthermore, the cost of the labor for installing equipment using a transformer for each tube would be objectionably high because a separateV charge is made for each connection tothe source of supply.

In transformers I have heretofore designed for operating a luminescent sign or display, these objections are removed by placing two or more secondary windings in series upon a transformer Each winding comprises two coils and energizes one negative load. Each coil has associated with it a magnetic by-pass of high reluctance which limits the flow of current through the coil to a safe value. The major portion of the main magnetic flux passes through the bypass when the current owing through the coil reaches such a Value that it generates a countermagnetomotiveforce which is suiiicient to buck most of the main flux. As a consequence of the coils being mounted in series on the core, when v-the countermagnetomotive force of one coil causes the main flux to be by-passed through a shunt, the ilux then interlinking the remaining coils is no greater than it was before the first coil became loaded. In fact, due to the increased reluctance of its path, the flux coursing through the core will be somewhat diminished in amount. Consequently, the remaining coils will not have as high voltages induced in them as if they had become loaded first. Moreover, the instant at which the load of the remaining coils becomes operative lags substantially behind the time of striking of the first load.

One of the objects of my present invention therefore is to overcome the difficulties noted above and assure a substantially simultaneous striking of luminescent tubes although of slight equalities in voltage ratings.

It may be noted further that in the operation of a luminescent tube sign or display, conditions may be encountered which cause a short-circuiting of part or all of the apparatus. This may be caused by fog, rain, ice or other moist weather conditions in an atmosphere containing dust, mild sulphur-bearing agents in industrial areas, or salty particles Anear the seashore. 'Ihe apparatus may also be subjected to a certain amount of shock and vibration. Furthermore, it is not uncommon for insects to pack themselves around the tube electrodes and in between them and the supporting metallic structure, thus providing a conductive path around the tube. Under these conditions of operation, the tubes frequently become short-circuited from terminal to terminal or from terminal to ground.

Under the conditions of short-circuit, certain heretofore known and/ or used transformer apparatus, unless specially designed to accommodatev an excess current is inclined to excessive heating which results in the ultimate charring and burning of the insulation and the destruction of the transformer apparatus, necessitating shutdown and replacement or repair. This situation is especially prevalent in certain heretofore known and/or used transformer apparatus having the secondary winding grounded at its midpoint. When a luminescent tube energized by such transformer apparatus becomes grounded at one terminal, as indicated above, excessive current is` inclined to fiow in one half of the secondary winding while no current flows in the other half of the winding. The flow of excessive current damages ,the winding unless it is designed p use a separate transformer for each tube would to carry this heavy current. Such a design, of course, requires larger, heavier, and more expensive coils.

Accordingly, another object of my invention is to provide a transformer apparatus whichv is inexpensive in construction, employing windings of minimum necessary current-carrying capacity and of minimum cost, and yet which is of such construction as to reliably withstand the many varying conditions encountered in actual prac- 'tical use,

Referring now more particularly to the practice of my invention, attention is invited to Figures 1 and 2 of the drawings in which there is shown a transformer, generally indicated by the number i comprising a core, a primary winding, and two secondary windings adapted to be positioned in a suitable casing, if desired. The transformer core is preferably of laminated magnetic steel, and comprises two longitudinal bars ii and I2, la central core member I3, and

two H-shaped core members i4 and l5 mounted parallel to the central core member I3 and on opposite side thereof. Leg portions Ma and i5a of the H-shaped members it and i5 abut the bars i l 'and i2 atV a short distance from their ends. Legs Ilia and I5a are of substantially the same cross-sectional area`and hence are of substantially the same magnetic permcance. Each of legs Ma and i5a has a cross-sectional area which is approximately one half the cross sectional area of core member i3 and hence the magnetic permeance of each leg Mia and 15a is approximately one-half the permeance of core member i3.

The core member id has a central section ilic joining the leg portion ilia withV leg portion Mb which is somewhat shorter than leg Ma. Short leg portion Mb extends closely toward, but does not abut, the longitudinal bars ii and 1,2, respectively, at `or near their ends, forming therewith air gaps Gl and G2 of high and substantiallg;Y equal magnetic reluctances. Likewise, the core member i5 has a central portion ic which joins to the leg portion 15a a shorter leg portion i5b. The short leg portion i521, like the short leg portion Mib, extends closely toward, but does not abut, the bars il and i2, respectively, at or near their ends, 'forming therewith air-gaps G3 and tially the same cross-sectional area and hence have approximately equal magnetic reluctances. Hence the magnetic shunt paths for the separate secondary windings described hereinafter are of substantially equal reluctances.

When the tube loads are of different resistances, shunt paths of correspondingly diierent reluctances are employed. Thus, if the tube Ti, for example, requires a higher current density for its proper operation than the tube T2, as where tube Ti is of larger cross-sectional area than tube T2, the air-gaps GI and G2 will be made of greater width or of smaller area, or both, than the air-gaps G3 and Gli. Also, the short leg Mb may then be of smaller cross-sectional asians? 3 area and of correspondingly high magnetic reluctance than the short leg I Ib.l

Upon the central core member Il ismounted the primaryl coil P, which is energized from a source of single-phase alternating electrical current energy i6, such as the usual 110 volt or 220 volt commercial source, through leads Il and II. Secondary coil sections SI and S2 forming one secondary winding are mounted on long leg portion Ila at its ends and on opposite sides of the central section llc and of the primary coil P, which, as shown, extends between the secondary coils. Secondary coils S2 and S4 forming another secondary winding are likewise mounted on the ends of long leg portion lia on opposite sides of the central section lic and of primary coil P.

One terminal of secondary coil SI is grounded to the core at I9. The other terminal is connected by a lead 2l to one terminal of a iluorescent luminous tube TI. Likewise, one terminal of the coil S2 is grounded to the core at 2l and its other terminal is connected to the other terminal of the tube TI by a lead 22. The coils Si and S2 are connected in a series relationship. 'I'he potential appearing across the output terminals of the secondary winding Si-SZ is therefore equal to, the total of the values of the electromotive forces induced in the individual coils Si and S2 with respect to their ground connections.

Where the load comprises two or more tubes connected serially, the coils may be connected in a bucking relationship, in which case the approximate central point of the load must be grounded With the coils Si and S2 connected in a bucking relationship, as the electromotive force in coil Si, for example, is rising to a maximum value in a positive direction, the electromotive force induced in coil S2 is also rising to a maximum value in a positive direction. The output terminals of the secondary winding SI-S2 are therefore always at substantially the same potential and a ground or connection to the coil midpoint must be placed at the load midpoint to form a complete circuit through each half of the load.

Coil S3 is grounded at one end to the core as at 23. Its other terminal is connected to a second luminous tube T2 by a lead 24. Similarly, one terminal of the coil S4 is grounded at 25 and its other terminal is connected by a lead 26 to the other terminal of the tube T2. In order that the potential of no coil section may reach an excessively high value to ground, the core itself is grounded, as at 21. The core parts may be held together by straps 28 and 29 of non-magnetic material.

The tube T2 may be formed with an arcuate grooved recess in which the tube TI fits so that the light rays of different colors from the two tubes may be blended to form light of one color, such as white light for example.

The tube Tl is of approximately the same length and electrical characteristics as tube T2. Likewise, the secondary coils Si, S2, S3, and S4 are ordinarily made of Wire of the same diameter and have the same number of turns and thus have identical current and voltage ratings. Furthermore, the air-gaps Gi, G2, G3 and G4 are of substantially the same reluctance. In the no1'- mal operation of the system, therefore, it would be expected that the two tubes would become operative at about the same instant. In practice, however, one tube usually strikes before the other. In the use of the transformer of my invention, this differential in time of striking is minimized.

Moreover, the voltages impressed on the tubes are maintained at substantially equal values and are always in the same direction. Thus, condenser ei'fects betweenthe tubes are minimized and puncturing of the tube walls due to dielectric discharge is avoided.

Ordinarily, in the design of a luminescent sign or display, the complete display is made up of a number of luminescent tubes or series oi tubes of various configurations which are as near the same total length as is conveniently practicable. In energizing two tubes comprising a part oi such a display the secondary windings of my transformer apparatus are preferably of about the same voltage rating as a matter of convenience in production ot the apparatus, although better results in operation are achieved where the ratings of the secondary windings conform exactly to the ratings of the individual luminescent tubes which they are intended to operate. In the event the loads are of different electrical characteristics, the winding for the load of higher resistance will comprise coil sections oi heavier wire and having a greater number of turns and consequently higher current and voltage ratings.

also, the shunt path associated with the higher i potential winding will be of greater reluctance, the shunt arm being of smaller cross section, thus increasing its reluctance, or the reluctance of the included air-gap being increased.

It is to be noted at this point that my transformer apparatus is exceedingly compact and rugged in construction. The various secondary winding coil sections snugly fit within the spaces provided for them by the opposite C-sliaped openings in the H-shaped core members. Similarly, the primary coil section iits snugly within the space provided for it between the secondary coil sections and between the long leg portions of the H-shaped members. With this construction, a minimum amount oi iron is required in the core, thus effecting a very real and direct economy. Io hold the different parts of the transformer together only two core bands and two wedges are necessary. Furthermore, with this construction the overall dimensions of the transformer apparatus are reduced to a minimum. The cost of an enclosure for the transformer apparatus and the packaging and shipping costs incident to the transportation of a large number of the units are thus effectively minimized.

In the transformer of my invention the windings energizing separate loads are placed upon core members forming parts of separate magnetic paths which are in parallel relationship. When one load strikes and the maj-or portion of the main flux is thereafter shunted around its winding, there remains a parallel path of .low reluctance through the winding or windings of the tubes which have not yet become operative. Thusx not only the normal amount of the flux but an added amount diverted from the parallel path acts to energize the remaining unloaded tubes. Because of this arrangement, the voltage across the remaining loads is equal to or slightly higher than that across the first load, regardless of differences of electrical characteristics of the loads. Moreover, the time lag between striking of the iirst tube and of the remaining tube or tubes energized from the same transformer is reduced to a minimum.

This condition of substantially equal voltages across the various loads is of particular importance in the operation of luminescent tube signs .in which two or more luminescent tubes are placed in closev proximity for the blending of` their light rays. In such installations, differences of potential between' corresponding points along the lengths" of the two tubes vare to be avoided,

to prevent puncturing of the tubes by condenser action. In a system using a series type of transtential than the other.

do not occur because, as is explained above, the

voltages across adjacent tubes Aare substantially equal in value and the tubes are so connected that the potentials are inthe same direction in the tubes at the same instant. Y

In the operation of the transformer of Figures l and 2, the primary coil P generates a iiux in the core'piece I3 as the electromotive force from the source I6 rises in either direction from a zero value. During one cycle of the impressed electromotive force the flux will course upwardly through core piece I3 into bar I2 where it will divide into two parts, one part goingto the left and the other part going to the right in bar I2. The one part of the uX will then course through long leg portion I4a, interlinking secondary coils S2 and SI, and generating an electromotive force in them. From portion Ida, the ux then courses into bar Il, through it into member I3, where it reunites with the other part of the ilux. The other part of the ux goes from bar I2 into long leg portion 15a where it interlinks coils S4 and S3 and induces in them an electromotive force. The flux in portion a then goes into bar II and through it into member I3 where it reunites with the nrst part of the iiux.

In normal operation of loads not grounded at their midpoints, there is no coursing of the magnetic ux across the central sections I4c and I 5c of the H-shaped core members I4 and I5. The coil SI isof the same current and voltage rating as coil S2, both being made of wire of the same diameter and having the same number of turns. Likewise, coils S3 and S4 are identical. Also, the air-gaps GI and G2 are of the same reluctance, as are the air-gaps G3 and G4. Therefore, when the gas in one tube, for example tube TI, is ionized and conductive, the current through coil SI is the same as that through coil S2, and, each having the same number of turns, the back magnetomotive forces generated by each will be the same. 'Therefore, the reluctance of long leg Ilia will be the same at each end. The reluctance of short leg l4b and its associated air-gaps also being the same at each end, the flux will divide and course equally through the'whole lengths of the two legs in inverse proportion to the reluctances of the paths through them, and no ux will pass through section I4c. Likewise, the same amount of ux will course through both ends of leg 15a at all times during normal operation and none will pass through section I'5c.

As illustrated, the cross-sectional area of lthe transformer member I3 is approximately twice that of either long leg I4a or 15a. Since the magnetic flux from member I3 divides substantially equally between legs I4a and I5a, the voltage per turn induced in each of the coil sections SI, S2, S3 and S4 is approximately one-half the voltage drop per turn in the primary winding PI.

The tubes TI and T2 are of equal length and in theory their resistance should be the same. In practice, however, due to variations in the density of the gas caused by occlusions in the'tube walls and due to variations in the gas pressure, one tube usually loperates at a somewhat lower po- Assuming that tube TI operates at a lower potential than tube T2, tube TI will strike first and a current will ow through coils Si and S2. Thiscurrent will not reach an excessively high value when the tube TI becomes ionized and highly conductive because of the magnetic shunt construction provided. When current ilows in the coils SI and S2, it sets up in the leg Ilia acounter magnetomotive force which bucks the main ux and causes it to seek a path of lower reluctance. Until tube T2 strikes such a path is found through the long leg I5a. The flux diverted from coils SI and S2 becomes added to the flux already linking coils S3 and S4 so that the electromotive force induced in them is higher than that induced in them by their normal share of uX. Due to this cumulative eiect of the iiux, the tube T2 strikes very soon after tube TI. The difference between the striking potentials of tubes TI and T2 will be small where the tubes are of substantially the same length and the gases in them are at about the same pressure, in spite of minor variations caused by occlusions of gas in the tube walls.

Due to the particularly advantageous operation of my transformer in causing the tubes to become ionized at substantially the same instant, the voltages along contiguous portionsof the respective tubes will be substantially equal at all times during the complete cycle 4of operation. Consequently, condenser effect between the adjacent tubes is either eliminated or substantially minimized so that no discharge occurs between them.

The flux diverted from long leg ida of member I4, when tube TI strikes, will interlink coils C3 and S4 because the magnetic reluctance of leg Ilia has become greater than that of long leg I5a of member I5. The reluctance of leg I5a before tube T2 strikes is less than that of the magnetic by-pass around coils SI and S2. This by-pass is from bar I2 through air-gap G2, short leg Ib, air-gap GI, bar I I, and member I3 back to bar I2. When both tubes TI and T2 have struck, however, the path of least reluctance for the ux is then through the magnetic shunt described above for the winding comprising coils SI and S2 and through the corresponding shunt path for the coils S3 and SLI. The latter shunt path is from bar I2 through air-gap G4, short leg 15b, air-gap G3, bar II, member I3 and back to bar I2. When both tubes are operating, the major portion of the flux passes through these magnetic shunts. Enough iiux still interlinks the coils, however, to maintain a steady ow of current through the tubes. Thus the current in the tubes is prevented from rising to an 'excessively high value and safe operation of the system is automatically assured, there being no danger of burning out the secondary coils or their connections by overloading them. Since the shunt paths are of substantially equal magnetic reluctances, the currents flowing in the separate secondary windings and their loads are substantially equal in spite of variations in electrical characteristics of the loads. Due to substantial equality of currents through the loads and to the aforementioned substantial equality of potentials across the loads, dielectric discharges between adjacent tubes are eliminated. Y

The luminous condition of tube TI persists until the potential output of secondary winding SI-S2 falls to a value insufcient to maintain the ionized conditionl of the tube as a result of a falling of the electromotive forces induced in coil sections SI and S2 by virtue of the changing magnetic flux in the transformer core caused by the source of alternating-current supply continuing through its cycle of alternations. At this time the tube becomes suddenly unionized and non-conductive and current ceases to ilow in the secondary Winding and the back magnetomotive forces suddenly fall to zero. The magnetic iiux tends to course through bars I I and I2 and the long leg I4a of H-shaped section I4 through the path of low reluctance. Because of the comparatively high reluctance of the magnetic path through the air-gaps GI and G2 substantially no flux appears in the short leg I4b of the H-shaped core member at this time.

With the continued change in the magnitude and direction of the magnetic flux coursing through the transformer core and interlinking the primary and secondary windings, the electromotive forces induced in the coil sections comprising the transformer secondary winding SI-S2 fall through zero and rise in the opposite direction causing the output potential of the secondary winding representing the difference between these induced electromotive forces to again reach a value sucient to establish an ionized condition. The gas column present in tube TI renders the tube conductive and luminous and again the ilo-w of excess current in the transformer secondary winding is effectively prevented by the appearance of back magnetomotive forces causing the major portion of the magnetic flux to ilow through the path interlinking the other Secondary winding S3-S4, if its load is not yet operating or through the shunt path of high reluctance across air-gaps GI and G2 and the short leg I4b if the load of winding S3S4 is operating.

Since the output potential of the transformer secondary winding reaches a maximum twice for each cycle of the source of alternating current electrical energy, the tube TI becomes luminous twice for each complete cycle of the source or one hundred and twenty times a second where a sixty cycle source is employed. Due to the persistence of vision the luminescent tube appears to give forth a continuous glow.

It will, of course, be understood that luminescent tube T2 operates in a manner exactly similar to thatof tube TI, in accordance with variations in the output potentials of the secondary winding S3-S4 and its related magnetic circuit including bars I I and I2 and the H-shaped core member I5 with its short leg I5b providing a shunt path of high reluctance around this winding.

It may happen that one of the tubes becomes short circuited due to a lm of moisture, dirt, matted insect bodies, etc., forming a conductive exterior path between its terminals. Assuming that tube TI has thus become shorted, the operation of the other tube will n ot be interfered with nor will there be any danger of excessive current through the short circuit. This is because the current ilowing in coils SI and S2 will act precisely as it does when tube TI is operating normally. That is, the current in the coils will generate a countermagnetomotive force which will buck the main flux and divert most of it to the other coils S3 and S4 if tube T2 has not struck or through the magnetic lay-passes 1f tube T2 has struck. Thus, if tube T2 is lighted, the flux diverted from long leg I4a will pass from bar I2 through air-gap G2', short leg I4b, airgap GI, bar II, and member I3 back to bar I2. In either case, the current flowing between the shorted terminals of tube T and through its secondary winding will not exceed the amount flowing through that tube when it is operating normally.

Likewise, if tube T2 becomes shorted, the flux linking its secondary coils S3 and S4 will be `largely diverted either to link the coils Sl and S2 or, if the gas in the tube TI is already ionized, through the by-pass comprising air-gap G4, short leg I5b, and air-gap G3. Thus the current between terminals of the shorted tube T2 will be limited to a safe value.

Should the tube TI become open circuited, as through breaking of the tube or of a connection, obviously no current will ilow through its circuit and no dangerous condition of excessive current Will exist. At the same time, the tube T2 will continue to operate normally. When the winding comprising the coils SI and S2 is open-circuited, the main ux will course, as in normal operation when neither tube has yet become operative, through the parallel magnetic paths until the gas in tube T2 becomes ionized and conductive; at that instant, the major portion of the iiux will then course through the magnetic path of least reluctance. That path will be from the member I3 through the bar I2, the long leg I4a, interlinking the open-circuited coils SI and S2, and through the bar II back to the member I3. Due to the relatively small cross-sectional area of the leg I4a, which is designed to carry only half the flux generated by the primary coil P, the flux will not be entirely diverted through it but some of the ilux will pass through the shunt path from member I3 through bar I2, air-gap G4, short leg I5b, air-gap G3, and bar II back to member I3 and/or through the other shunt path from member I3 through bar I2, air-gap G2, short leg I4b, air-gap GI, and bar II back to member. I3. There will still be suiicient flux coursing through long leg 15a and interlinking coils S3 and S4 to maintain a steady flow of current through the tube T2. However, the value of this current may be somewhat below its Value when the system is operating normally. The same condition of operation will prevail if it is the tube T2 which becomes open-circuited.

In the event that one coil becomes shorted, say the coil SI, it will not carry an excessive current. As current begins to ow in it, due to the electromotive force induced in it rising from a zero value, a countermagnetomotive force will be generated which will divert the main flux from long leg Illa around the shunt path from leg Illa through central section I4c, short leg I4b and air-gap GI, from whence it goes through bar I I, member I3, and bar I2 back to long leg I4a. Of course, if the load of the winding comprising coils SI and S2 is a single tube, as the tube TI illustrated, it will not be rendered operative Whenthe coil SI is grounded. The voltage induced in the other coil S2 will not be suilicient to cause the gas in tube TI to becomes ionized. If, on the other hand, the load of the winding SI, S2 comprises two or more tubes in series which are grounded at a point within 15% of the level of mid-potential of the whole series, a complete circuit will exist between coil S2, and its portion of the load so that that portion will be operative.

If .the coil S2 becomes grounded, excessive current will not ilow in it because the main flux will be diverted through air-gap G2, short leg portion Mb, and central section Mc to the lower half of long leg I4a. Likewise, if either coil S3 or S4 is grounded, the main flux will be by-passed from long leg portion Ia through central section I5c, short leg lib, and air-gap G3 to bar H when S3 is grounded or through air-gap G4, short leg b, and central section -l5c to the lower half of longv leg I5a when S4 is grounded.

If one secondary coil, for instance coil Sl, is open-circuited, the whole winding will be opencircuited if the load is a single tube, as the tube Tl, and no current will flow in the load but the other tube T2 will continue to operate, as has been fully set out above. If, on the other hand. the load comprises two or more tubes grounded at their approximate mid-point, that portion of the load corresponding to the coil S2 will be energized and will operate in the normal manner, as will the load of the coils S3 and S4.

Likewise, if any of the other coils, S2, S3 or S4, becomes open-circuited, the whole load of its winding will be open-circuited and inoperative if it comprises only a single tube, but the load of the other winding will continue to operate. If the load of the winding including the open-circuited coil comprises two or more tubes grounded at their mid-points, that part of the load corresponding to the other operative coil will be energized in a, normal manner, as will the load of the other winding.

Similarly, under the possible operating conditions of one coil section being grounded, for example SI, and the other vbeing substantially open-circuited, for example S2, the major portion of the magnetic ilux courses along a path of intermediate magnetic reluctance, including the core bars il and l2 and the H-shaped member i4. and passes between the coil sections Sl and S2 by way of the central section Mc of the H- shaped member and across the air-gap Gi, including and interlinking the coil section S2 operating under open-circuit conditions but excluding and passing around the short-circuited coil section Si to efect a limitation in the amount of magnetic ux linking the short-circuited coil section Si and thereby preventing the current in this section from reaching an excessive value. A similar condition of operation will obtain in the other possible situations of the grounding of any other coil section and the opencircuiting of the other coil section forming part of the same winding.

Where the load of a Winding comprises not a single tube but two or more tubes in series and having their mid-points grounded, the advantages of my invention may be had if the coils of the transformer are connected together in different manners. For example, the coil Sl may be connected with coil S4 in either series-aiding or series-opposition phase relationship. Likewise, coil S2 may be connected with coil S3 in series-aiding or series-opposition relationship. Any other combination of coil sections may be used or each coil section may energize its own individual load, uncombined with any other coil section.

It is to be noted at this point that in my electrical transformer apparatus only a single primary winding and a single core structure are employed. The total magnetic flux is created by the one primary winding and, by Way of the single core structure, serves to link and energize both secondary windings. This construction, of course, effects a direct saving in construction l over heretofore known transformer apparatus.

It is to be particularly noted, however, that these savings in iron, for the core, and copper, for the primary winding, do not result in a loss in operating elciency or, of greatest importance, in a risk of damage to any coil of the secondary winding as a result of accidental grounding of such a coil. Especially is it to be noted that protection of the secondary winding coil sections is achieved without necessity for increasing the size of wire over that normally necessary to handle the operating current of the luminescent tubes. These savings and economies in the construction of a single piece of apparatus requiring but a single connection to a source of supply energy are of the greatest practical importance in the operation of a maximum length of luminescent tubes by a single piece of apparatus.

A further practical advantage of my transformer apparatus is that, the potential to ground in no part of the system exceeding a certain value, a minimum of expensive insulation is required for the various leads. In this manner, further economies are eiected.

Considering now another embodiment of my invention, attention is directed to Figure 3, in

which I show a' transformer having the magnetic shunts for the secondary coils located internally of the main core. by reversing the positions of the H-shaped core members. The transformer 3Q comprises laminated longitudinal bars 3| and 32 which are abutted by central transverse member 33 and by the long leg portions a and 35a of H-shaped members 313 and 35. The central Asection 34o o f the member 34 joins long leg portion 34a and short leg portion Slib, which forms air-gaps GI and G2 with the bars 3l and 32 respectively. Likewise, the central section 35e of the member 35 joins the long leg portion 35a and the short leg portion 35D, which forms air-gaps G3 and Gl with the bars 3l and 32, respectively.

Mounted on the transverse member 33 is the primary coil P which is energized from a source of alternating current electrical energy 35 through leads 3l and 33. On the long leg portion 36a of section 34 are mounted the secondary coils Si and S2, which form one secondary winding. Coil Sl is grounded tothe core at one end as at 39 and the other terminal is connected by lead d to one terminal of a negative load, such as a iluorescent luminous tube Ti. One terminal of coil S2 is likewise grounded, as at fil, so as to place the coils Si and S2 in series-aiding relation if the load is a single tube, or in either series-aiding or series-opposition relation if the load comprises two or more tubes grounded at their mid-point. The other terminal of coil S2 is connected by lead $2 to the other terminal of the load. Similarly, coils S3 and S, comprising another secondary winding, are mounted on the long leg portion 35a of section 35 and are grounded to the core at their one ends at 43 and i6 respectively. They are also connected so as to be either in series-aiding or series-opposition relationship and energize a negative load, such as the luminescent tube T2, through leads id and d5.

The core parts are held together by bands d6 and 49 of non-magnetic material and the core is grounded as at 41. The essential difference between the transformer of Figure 3 and that oi Figures l and 2 is that the former has its magnetic shunts located internally of the core. The operation of the two transformers is identical except that when the main ilux is icy-passed This change is eiected merely around one or more secondary coils, the path it follows will be internally of the core.

Thus, during those periods when the luminescent tube loads of the two windings are in their un-ionized non-conductive states, the magnetic flux interlinking the primary and secondary windings courses along the two parallel long paths of low reluctance including the member 33, the longitudinal bars 3| and 32, and the long legs 34a and 35a. During those brief periods when either or both of the luminescent tube loads are in their ionized conductive conditions, the major portion of the magnetic flux, normally passing through one path, courses through the other path or along a short shunt path of high reluctance around and excluding the coil sections comprising the secondary windings which supply high potential electrical energy to the tube or tubes in the conductive state. During the conductive state of the load supplied by coils Sl and S2', for example, the major portion of the magnetic iiux, coursing from member 33 through bar 32, long leg 34a, and bar 3|, is diverted from that path into the path from member 33 through bar 32, long leg 35a and bar 3|. adding to the ux already interlinking the other coils S3 and S4 if the load of those coils is not yet operating. If the tubes in the load of coils S3 and S4 are already ionized and conductive, the ux diverted from the path of the coils Sl and S2 will pass from member 33 through bar 32, air-gap G2, short leg 34h, airgap GI, and bar 3|, back into member 33. Similarly, the flux diverted from the path through member 33, bar 32, long leg 35a, and bar 3| back to member 33 when the load of coils S3 and S4 is rendered operative will pass through the leit hand path including long leg 34a and interlinking the coils S| and S2 if the load of those coils has not yet become ionized and conductive. If the load of coils SI and S2 is already operating, thcux diverted from the path of coils S3 and S4 will pass from member 33 through bar 32, air-gap G4, short leg 35h, air-gap G3, and bar 3| back to member 33.` When both loads are operating, therefore, the major portion of the flux will be diverted into the two short magnetic paths which include air-gaps of high reluctance. The remaining portion of the ilux, which continues to interlink the secondary coils with the primary coil, will be adequate, however, to `maintain an induced potential in the coils sufficient to maintain a flow of current through the luminescent tubes and to preserve brilliant operation.

In the event of a short circuit occurring across a whole secondary Winding, the coursing of the magnetic flux through the core of the transformer apparatus is substantially the same as it is during the conductive periods of its load. The amount of current owing in the winding in this condition of operation is about the same as that encountered under normal operating conditions. In neither condition of operation does this current rise to such excessive Values as to cause objectionable heating and damage to the coils.

In the event that only one coil section of a secondary winding becomes grounded, the iiow of an excessively high current in this coil section is effectively prevented, in a manner more particularly described above, by the major portion of the magnetic flux coursing along a path of intermediate reluctance provided by a shunt arm and its associated air-gap. This path extends around and excludes the short-circuited coil section and includes and links the complementary open-circuited coil section. The portion of the total magnetic flux that interlinks the primary winding with the short-circuited coil section is substantially the same as that inter-linking these two under normal operating conditions or under short-circuited operating conditions of the entire secondary winding. In all instances, the electromotive forces induced in the secondary winding are not so great as to cause the flow of an excessively high current in the coil sections of this winding.

The transformer shown in Figure 3 has the same compactness and symmetrical ux and current distribution as the transformer of Figures 1 and 2. However, due to the internal location of the shunt air-gaps in the former, there will be less fringing of the magnetic ilux to the casing. Consequently, better control of the airgap reluctances will be possible.

A transformer having a construction slightly modified from that of the transformer of Figure 3 is shown in Figure 4. The principal difference is that in the former the secondary coils are mounted on the longitudinal bars instead of on the long leg portions of the H-shaped pieces as in the latter construction. In both forms, the H-shaped pieces are so disposed that the magnetic by-passes are located internally of the main core. 'I'he operation of this transformer is identical with that of the transformer of Figure 3.

The advantage of this form of transformer. in addition to the compactness and balance of flux and currents noted with regard to the other forms, is that it is more easily assembled. The parts are so disposed that the work of assembly may be performed in a few simple operations. Furthermore, the casing will be shorter and broader, so that it may be tted into a space which would not accommodate the other forms. While, as illustrative of my invention, H- shaped transformer core members having long and short leg portions of equal width are indicated, it will be understood that where desired the short leg portions may be either of greater widths or lesser widths. In fact, in order to gain a maximum compactness of construction and employ a minimum amount of core material consistent with good operating characteristics, the short leg portions of the H-shaped members are preferably made of a lesser width than the long leg portions, the relation between the Widths of the two leg portions, or sectional areas, since the thickness of the member is constant, being in accordance with the relation between the total magnetic flux and that major portion which is shunted around and about the coil sections during certain of the operating conditions indicated above.

Another embodiment of my invention is indicated in Figure 5. In this modification, the transformer core 50 includes the laminated longitudinal core bars 5| and 52 and the transverse bars 54 and 55 abutting the ends of the longitudinal bars. In the space formed internally by the above mentioned bars, there is a central member 53 whose ends abut the longitudinal bars 5| and 52 and which lies parallel to the transverse bars 54 and 55. Projecting from either side of the member 53 are integral shunt arms 53a, 53h, 53e and 53d, which extend closely toward but do not abut transverse bars 54 and 55, forming therewith air-gaps GI, G2, G3 and G4 respectively of high and substantially equal magnetic reluctances.

On the member 53, between the shunt arms 53a and 53h on the one side and between shunt arms 53e and 53d on the other side, is mounted the primary coil P. This coil is energized from a suitable source of alternating current electrical energy 56 through leads 5l and 58.

The secondary coil SI is mounted on the longitudinal bar l between the member 53 and the transverse bar 54 in the space between the bar 5I and the shunt arm 53a. One terminal of this coil is grounded to the core at 59 and the other terminal is connected by lead 60 to one terminal of a negative load, such as the tube Tl. The coil S2, forming with coil SI a secondary winding, is mounted on the longitudinal bar 52 between the member 53 and the transverse bar 54 in the space between the'bar 52 and the shunt arm 53h. One terminal of coil `S2 is grounded to the core at 6|, placing coils Si and-S2 in series-aiding relationship if their load is a single tube, or in either series-aiding or series-opposition relationship if the load comprises two or more tubes grounded at their mid-point.

The other terminal of coil S2 is connected by lead 62 to the other terminal oi the tube TI.

Similarly, the coil sections S3 and S4, forming another secondary winding, are mounted on the longitudinal bars 5| and 52 respectively, between the member 53 and the transverse bar 55. Their one terminals are grounded to the core at 83 and 65, respectively, placing the coils in either seriesaiding or series-opposition relationship. Their other terminals are connected by the leads 64 and 6B to a negative load, illustratively the luminous tube T2.

The core is grounded at '6l and its parts are held together by core bands 68 and B3 which may be of either magnetic or non-magnetic material, but preferably magnetic.

In the operation of this transformer, as the current in the primary coil P rises from the zero value in one direction in one cycle of the impressed electrornotive force, a ux is generated in the member 53. Assuming that this iiux ows from right to left in the member 53 at the instant under discussion, upon reaching the bar 5I it will divide into two substantially equal parts.

One of these ows downwardly through the lower portion of bar 5l, linking coil Si, then throughA bar 54, downwardly through the lower part of bar 52 linking coil S2, and back through bar 53 linking primary winding P. The other path of the ilux is through the upper part of bar 5|, thus linking coil S3, through bar 55, downwardly through the upper part of bar 52, thereby linking coil 34, and -then back through core piece 53 and so linking primary coil P. It will be seen that the two flux paths reunite and flow together through core 53.

The operation of this transformer under the various conditions of normal operation, short circuit of one or both coils of a winding, and the like, is the same as that described in connection with the transformer of Figures 1 and 2.

Thus, during those periods when the luminescent tube loads of the two windings are in their un-ionized non-conductive states, the magnetic ux interlinking the primary and secondary windings courses along the two parallel long paths of low reluctance including the member 53, the longitudinal bars 5l and 52 and the transverse bars 54 and 55. During those brief periods when either or both of the luminescent tube loads are 76 in their ionized conductive conditions, the major portion of the magnetic flux, normally passing through one long path, changes its path and courses through the other long path upon one tube being rendered conductive, and further changes its path when the other tube also is rendered conductive to iiow along a short shunt path of high reluctance around and excluding the coil sections comprising the secondary windings. During the conductive state of the load of coils Si and S2, for example, the major portion of the magnetic iiux normally coursing through member 53 and lower part of bar 5|, bar 54 and lower part of bar 52, is diverted from that path into the path from member 53 -through the upper part of bar 5I, bar 55, and upper part oi bar 52, adding to the ux already interlinking the other coils S3 and S4, if the load of those coils is not yet operating. If the load of coils S3 and S4 is already operating, the flux diverted from the path of coils Sl and S2 will pass from member 53 through shunt arm 53a, air-gap GI, bar 54, air-gap G2, and shunt arm 53h back into member 53. Similarly, the ux diverted from the normal path through member 53 and upper part of bar 5 I bar '55 and upper part of bar 52 back to member 53 when the load of coils S3 and S4 is rendered operative will pass through the lower portion of bar 5l, bar 54 and lower part of bar 52, thus adding to the flux already interlinking coils Si and S2 if the load of those coils has not yet become ionized and conductive. If the load of coils Si and S2 is already operating, the flux diverted from the path of coils S3 and S4 will pass from member 53 through shunt arm 53o, air-gap G3, bar 55, air-gap G4, and shunt arm 53d back to member 53. In other Words, when both loads are operating the major portion oi the flux will be diverted into the two short magnetic paths which include air-gaps of high reluctance. The remaining portion of the flux, which continues to interlink the secondary coils, is adequate, however, to maintain an induced potential in the coils suicient to maintain a flow of current through the luminescent tubes and to preserve brilliant operation.

Thus in the transformer of Figure 5, the advantages of my invention are fully obtained. The out-put voltages of the separate secondary windings are maintained at substantial equality throughout the entire cycle of operation and due to the peculiar construction of my transformer the negative loads of the separate secondary windings are rendered operative at substantially the same instant.

In the event of a short circuit occurring across a whole secondary Winding, the coursing of the magnetic flux through the core of the transformer apparatus is substantially the same as it is during the conductive periods of its load. The amount of current flowing in the winding in this condition of operation is about the same as that encountered under normal operating conditions. In neither condition of operation does this current rise to such excessive values as to cause objectionable heating and damage to the coils.

In the event that only one coil section of a secondary winding becomes grounded, the flow of an excessively high current in this coil section is eiectively prevented, in a manner more particularly described above, by the major portion of the magnetic flux coursing along a path of intermediate reluctance provided by a shunt arm and its associated air-gap. This path extends around and excludes the short-circuited section. The portion of the total magnetic flux that interlinks the primary winding with the short-circuited coil section, that is the minor portion of the flux, is substantially the same as that interlinking these two under normal operating conditions or under short-circuited operating conditions of the entire secondary winding. In all instances, the electromotive forces induced in the secondary winding are not so great as to cause the flow of an excessively high current in the coil sections of this winding.

The transformer of Figure has internal shunt paths which will not be appreciably affected by the casing. The casingLbeing oppositeY only a small portion of the air-gap, will have little bridging effect. Thus good air-gap control is possible. Moreover, the transformer is made of simpler parts, which can be readily manufactured and assembled.

Still another embodiment of my invention is illustrated in Figure 6. This is what I term a single transformer, as distinguished from the double transformers of Figures 1 and 2, 3, 4 and 5, in which but two secondary coils, in addition to the primary coil, are mounted on the transformer core. The core comprises transverse bars 1| and 12 of laminated magnetic material, between which are interposed the longitudinal bars 13 and 14. 'I'he bar 13 has a central extension 13a which abuts the bar 14 and two shunt arms 13b and 13e which extend closely toward, but do not abut, bar 14, forming therewith airgaps GI and G2, respectively, of high magnetic reluctance. The core is grounded at 1.5.

The primary coil P is mounted on the central extension section 13a and is energized from a source of alternating current electrical energy 'I6 through leads 11 and 18. The secondary coil S| is mounted on the bar 1| and secondary coil S2 is mounted on bar 12. Equally good results may be achieved if the coils SI and S2 are mounted on the ends of the bars 13 or 14. One terminal of coil SI is grounded to the core at 19 and the other terminal is connected to one terminal of a negative load by lead 20. Likewise, one terminal of coil S2 is grounded to the core at 8| and its other terminal is connected to the other terminal of the negative load by the lead 82. The core parts are held together by bands 83 and 84 which are preferably of magnetic material.

The load of this transformer preferably com` prises two or more luminescent tubes, such as the tubes TI and T2, which are connected in series by a lead 85. The flux generated by primary coil P divides into two substantially equal parts, each of which links one secondary coil. These two coils are connected in series with the interconnection preferably grounded or they may be connected in a bucking relation forming two separate electrical circuits with the load. Where this latter connection is used, the load mid-point is grounded as at 86 or connected to the midpoint of the coils, as by a lead 81, so that a complete circuit is formed between each half of the load and the corresponding secondary coil, As current begins to ow in one coil, say coil S| a counter magnetomotive force is created in the bar 1| which bucks the main flux and causes it to seek a path of lower reluctance. If the half of the load corresponding to coil S2 is not yet energized, such a path is found through the bar 12, where the flux diverted from coil SI adds to the flux already interlinking coil S2. When both coils SI and S2 have current flowing through them, the magnetic paths of least reluctance are the shunt paths provided by the shunt arm 13b and air-gap GI for coil SI and shunt arm 13C and air-gap G2 for coil S2. It will be understood that with coils Sl and S2 connected in series, and supplying a single' load, no grounding of the mid-point of the load is required. Also, that the same current will flow in each coil and that under normal operation a symmetrical condition in both the magnetic Yand the electrical circuits will obtain.

The transformer of Figure 6 operates in a manner similar to that described in connection with the transformer of Figure 5, with the exception that there are only two secondary coils and two corresponding magnetic shunt paths. In both modifications, the advantages of my invention are obtained. The coils SI and S2 have induced in them voltages high enough to energize their respective portions of the load at substantially the same instant, where a bucking connection is used and the load-mid-point is connected to the common connection of the two coils as by grounding them. There is substantial equality between the output voltages of the secondary coils. No danger exists of excessive current flowing through either coil because of the peculiar magnetic shunt construction provided. Perfectly safe and economical operation is assured for all conditions of short-circuiting, grounding, or open-circuiting of all or any part of the load of one or both coils.

This modification of my transformer has the advantages hereinbefore noted in connection with the other forms of my invention, namely, compactness of construction, symmetry of iiux and current distribution, and safe operation under conditions of short and open circuits. Furthermore, for a single tube load, or a load comprising two or more tubes not grounded'at their midpoint, where the secondary coils are connected series-aiding, a high output potential is obtained with nevertheless no more than a safe maximum potential to ground. Where the load comprises two or more tubes which are grounded at; their midpoint and the secondary coils are connected in series opposition, a condition of balanced voltages and currents across the two halve of the load will obtain. There will be dependable operation of each half of the load and a minimum time lag will exist between the striking of the two halves. Dielectric discharge between the two halves of the load is eliminated. Moreover, the transformer is made of a minimum number of relatively simple parts which are readily assemble-d. Finally, the advantage of an internal shunt construction, that is, a minimum of fringing to the casing, is obtained.

A slight modification of the transformer of Figure 6 is shown in Figure '7. The transformer, generally indicated by the reference character 90, comprises the longitudinal core bars 93 and 94, upon which are mounted primary and secondary windings as noted below, and also the short core members 9| and 92 interposed between the ends of the longitudinal bars. The bar 93 has a central extension 93a which abuts the bar 94. Bar 93 also has integral shunt arms 93h and 93e which are of greater width and area than the shunt arms 13b and 13o of the transformer shown in Figure 6 and which extend closely toward but do not abut bar 94, forming therewith air-gaps GI and G2. Because of the increased area of the shunt arms and the correspondingly increased surface of the air-gaps, the reluctances tween shunt arm 93h and member 9|.

of the shunt paths in this modification are substantially less than the reluctances of the shunt paths in the transformer of Figure 6. The member 9| interposed between the end part 93d of bar 93 and longitudinal bar 94 forms a magnetic path of low reluctance, the core parts being held in rm contact by the band |03, preferably of magnetic material. Likewise, the member 92 lnterposed between the end part 93C of bar 93 and the bar 94 forms another magnetic path of low reluctance, the core parts being held together by the band |04 which also preferably is of magnetic material.

The primary coil P is mounted on the central extension 93a of bar 93 and is energized from the source of alternating current electrical energy 96 through leads 91 and 98.

Secondary coil Sl is mounted on the end part 93d of bar 93 at the point where a space is formed between part 93dv and bar 94 and be- One terminal of coil SI is grounded to the core at 99 and its other terminal is connected by lead to one terminal of a negative load. Coil S2 is mounted on the end part 93e of bar 93 at the point where a space is formed between part 93e and bar 94 and between shunt arm 93e and member 92. One terminal is` connected to load by conductor |0|. The other terminal of coil S2 is grounded to the core at |02. Coils Sl and S2 may be connected either in series-aiding or in series-opposition relationship, the transformer being more particularly designed, as is the transformer of Figure 6, for the operation of a load comprising a series of tubes, TI and T2, grounded at their approximate mid-point, as at |06. The load must be grounded at its approximate midpoint, or connected from the mid-point to the mid-point of the coils, as by the lead |01. if the coils are connected in series-oppositionin order that two complete circuits will be formed, one for each half of the load and its corresponding secondary coil. Where the coils are connected in series-aiding relationship, the load may be grounded at its mid-point to form a complete circuit for each half of the load with its secondary coil but this is inclined to cause an unbalanced operating condition for the transformer and for this reason ordinarily is omitted.

The operation of the transformer of Figure 7 is practically identical with that of the embodiment shown in Figure 6. The only difference is that, due to the decreased reluctance of the shunt paths in the transformer of Figure "I, there is somewhat better assurance against the rising of currents in the secondary coils to excessive values. In both modifications, however, I secure the many practical advantages of my invention which are hereinbefore set forth.

I'hus it will be seen that there has been provided in this invention transformer apparatus in which the various objects hereinbefore noted, together with many practical advantages thereof,

are successfully achieved. It will be seen that my transformer apparatus is exceedingly compact and rugged in construction and that it lends itself to inexpensive and efficient commercial production and installation, employing a minimum of different shaped core members and requiring a minimum of expensive dies, tools and equipment in its construction. It will be seen, further, that luminescent tubes of the maximum length energizable by any existing equipment approved by the Fire Underwriters are energized by my transformer without there being present any of the tube puncturing dielectric discharges frequently encountered in the use of present equipment. Moreover, my transformer meets the requirements of Fire Underwriters in that the potentiall from no point to ground substantially exceeds 7,500 Volts. In the operation of my transformer there is no possibility of overloading and consequent damage to the secondary winding in the event of accidental grounding of either 10 one or both coil sections of these windings.

While I have illustrated transformers having only one or two secondary windings and two or four coils, it-is to be understood that three or more windings may be employed with associated core portions and shunts, the additional secondary windings and core members being mounted out from the plane of the construction shown in the drawings for example. With the number of windings illustrated, however, the \transformer apparatus is exceptionally compact and yet, because of the peculiar core construction and the relation of this core to the secondary winding, it is fully protected from damage under the various conditions encountered in use. The compactness and coil protection feature assures an inexpensive, eilicient and thoroughly reliable piece of apparatus.

As many possible embodiments may be made of my invention and as many changes may be made in the embodiments hereinbefore set forth, it will be understood that all matter described herein, or shown in the accompanying drawings, is to be interpreted as illustrative, and not in a limiting sense.

I claim:

1. In electrical transformer apparatus of the character described, in combination, two linear core members spaced in parallel relationship, a f

transverse core member extending between and abutting said parallel members, two substantially H-shaped core members disposed one on either side of said transverse member each having a long leg portion so positioned as to abut the inner sides of said linear core members at points spaced froml the ends thereof to effect a closed magnetic circuit and each having a short leg portion so positioned as to form with the ends of said linear members a shunt path including air-gaps, a primary winding mounted on said transverse member, and two secondary windings each of which comprises two intermediately grounded coil sections mounted on said long leg portions of one of said H-shaped members with the primary winding physically disposed between the secondary windings and also between the coil sections comprising the secondary windings, whereby a compact and eiiicient transformer apparatus is achieved.

2. In electrical transformer apparatus of the character described, in combination, two linear 0 core members spaced in parallel relationship, a transverse core member extending between and abutting mid-points of said parallel members, two substantially H-shaped core members disposed one on either side of said transverse member each having a long leg portion so positioned as to abut the inner sides of said linear core members at the ends thereof to effect two closed magnetic circuits and each having a short leg portion positioned opposite points spaced from the ends of said linear members and forming with said linear members and the included airgaps magnetic shunt paths of high reluctance, a primary winding mounted on said transverse member, and two secondary windings each of which comprises two intermediately grounded coil sections mounted on said long leg portions of one of said H-shaped members with the secondary windings and the coil sections of each winding physically disposed on opposite sides of the primary winding and in symmetrical relationship therewith.

3. In electrical transformer apparatus of the character described, in combination, two parallel longitudinal core members, a transverse linear core member abutting said longitudinal .mem-

bers, at least two H-shaped core members dissaid transverse linear member a closed magnetic cirqiit, a primary winding mounted on said transverse linear member, at least two secondary windings, each comprising two coil sections connected together in series with mid-point grounded, mounted on the long leg portions of said H-shaped core members, said secondary windings and coil sections of each winding being physically disposed on opposite sides of the primary winding and in symmetrical relationship therewith, and the other leg portion of said H-shaped core members each forming a magnetic shunt associated with said coil sections.

CHARLES PHILIPPE BOUCHER. 

